Aircraft propulsion power plant



March 11, 1952 w R HAWTHORNE 2,589,078

AIRCRAFT PROPULSION POWER PLANT Filed March 27, 1945 Inventor AttorneyPatented Mar. 11, 1952 AIRCRAFT PROPULSION POWER PLANT William RedeHawthorne, Silver Spring, Md., assignor to Power Jets (Research andDevelopment) Ltd., London, England, a British com- Application March2'7, 1945, Serial No. 585,167 In Great Britain March 29, 1944 2 Claims.1 This invention relates to internal combustion turbine power plants ofthe type, referred to herein as double compound, having two mechanicallyindependent rotors capable of running at diiferent speeds, each of whichconsists of a compressor assembled as a single rotary unit with aturbine, and ducting interconnecting said rotors so that air passessuccessively and in the order named through the low and high pressurecompressors, combustion means in which fuel is injected and burntcontinuously, and the high and low pressure turbines in which thegaseous products of combustion are expanded so as to cause them to drivetheir respective compressors.

The references herein to engines of the type referred to is to be readas meaning an engine having the characteristics described in the foregoing, and as including modifications thereof in which the useful power,and in certain arrangements the efliciency also, is increased materiallyby employing reheating, which consists in injecting and burningadditional fuel in the gaseous combustion produtcs at a point or pointsbetween adjacent turbines or turbine stages; or in which power is alsotaken from a separate power turbine driven by the expanding gases. Themost efiicient and flexible operation of an engine of the type referredto is obtained where the high pressure turbine drives the high pressurecompressor and the low pressure compressor is driven by the low pressureturbine.

It is an object of the invention to adapt an engine of the type referredto for use as an aircraft propulsion unit driving a tractor propeller,that is, a bladed propulsion means which is at the leading end of theunit, considered in relation to the direction of flight. It is desirablein such a case that the propeller should be driven from the low pressureturbine in order to keep as low as possible the reduction ratio of anygearing between these elements. Difi'iculty arises, however, in the caseof a tractor propeller, particularly if an axial flow turbine isemployed, in achieving this desirable end whilst at the same timeattaining the degree of compactness demanded of an aircraft power unitand satisfying the further requirements that the low pressure turbineshould drive the low pressure compressor and must exhaust in adownstream direction, without introducin undesirable complication intothe ducting. All these difficulties are met in the present inwhichdrives the low pressure compressor, are located at'opposite ends of theengine with the low pressure turbine placed at the rear or downstreamend, and by driving the tractor propeller from the low pressure turbineby a power shaft which extends axially through the high pressure rotor.

Generally speaking, a reduction gear will be necessary in the propellerdrive in order to produce an acceptable revolution speed of thepropeller, depending on the characteristics of the latter. Where thegeneral design is such that critical whirling speeds of the propellershaft do not arise, the reduction gear may be placed in front of thehigh pressure rotor. According to a further feature of the invention,however, such reduction gear, or some stage thereof, is disposed betweenthe 10W and high pressure rotors. By so placing the reduction gearing orsome part of it, it becomes possible to ensure that the propellerdriving shaft will run at such a speed that critical whirling speeds inthis shaft, which would otherwise arise, are avoided.

This arrangement, although having the disadvantage of requiring a hollowhigh pressure rotor to accommodate the power transmission shaft for thetractor propeller, enables a power drive suitable for the latter to betaken from the low pressure rotor without necessitating a reversal offlow of the gases after passing through the low pressure .turbine, whichreversal of flow would entail such a pressure drop as would have aconsiderable adverse effect on the efiiciency of the engine. Also thearrangement enables the shafting between the low pressure turbine andlowpressure compressor to be kept short so that the danger of whirlingspeeds being reached is reduced considerably.

The invention is more particularly described with reference to theaccompanying drawing which is a half radial section and half sideelevation of a double compound engine for use as an aircraft propulsionunit driving a tractor propeller. In the embodiment illustrated in thedrawing the double compound engine comprises a low pressure axial flowturbine, a low-pressure axial flow compressor, a high pressure axialflow compressor, an annular combustion chamber, and a high pressureaxial flow turbine, all arranged coaxially, and in that serial orderfrom rear to front, within an engine nacelle Ill.

The low pressure turbine and the low pressure compressor have a commonrotor of composite form comprising a bladed turbine wheel I I and.abladed compressordrum l2 both fixed to an axial shaft l3'which ismounted for rotation in bearings I 4. The turbine wheel H operates in abladed turbine stator casing 15 which is supported from the rear bearingl4 by a diaphragm l6, and the compressor drum l2 operates in a bladedstator casing I! the rear end of which is secured to an inlet duct ringl8 having a rearward conical extension I?! supported by said rearbearing 14.

Similarly, the high pressure turbine and the high pressure compressorhave a common rotor of composite form comprising a bladed compressorrotor drum 29 connected by a forward conical extension 2! to a bladedturbine Wheel 22, this composite rotor being supported for free rotationabout a shaft 23, passing axially therethrough, by bearings 24, the rearbearing 24 supporting the rear end of the rotor drum 2!] through adiaphragm 25 and the forward bearing 24 being housed in the apex of theconical extension 2!. The rotor drum 20 operates in a bladed statorcasing 25, and the turbine wheel 22 operates in a bladed stator casing27; these stator casings 29, 27 are interconnected by a short duct ring28 and a cylindrical housing 29 which encloses the conical extension 2!of the rotor drum 29, the stator casing 27 being supported upon theshaft 23 by a bearing 30 immediately in advance of the turbine wheel 22and by a further bearing 31 in the apex of a forward conical extension32 secured to said stator casing 21.

An annular combustion chamber 33, into which fuel is injected and burnedcontinuously by burner jets 34 (only one of which is shown), connectsthe duct ring 28 to the inlet of the high pressure turbine casing 27,and the high pressure turbine outlet is connected through pipe ducting35 to the inlet of the low pressure turbine casing 15, said ducting 35extending through the nacelle l9 and being fitted with a reheater jet 39for injecting and burning fuel in the gas stream between the turbines.

Between the compressor portions of the two mechanically independentrotors is located a reduction gear 3'! which is driven by the shaft [3of the low pressure rotor and drives the shaft 23 which extendsforwardly and axially through the high pressure rotor, said reductiongear being mounted within a duct ring 38 which connects the flow annuliof the two compressors and is supported at its rear end by the forwardbearing I4 and integral disc 39 and at its forward end by a diaphragm 49and bearing 4| on the shaft 23. This shaft 23 drives the contra-rotatingelements 42, 43 of a tractor propeller located in advance of the enginenacelle Hi.

In operation, air is drawn into the engine, from the boundary layerpassing over the nacelle 10, through radial and forwardly directed inletducts 44 (only one of which is shown) leading to the duct ring l8, saidair passing through the low and high pressure compressors in series tothe combustion chamber 33. The gaseous products of combustion from thechamber 33 are partially expanded through the high pressure turbine soas to drive the high pressure turbine compressor rotor (20, 2!, 22, 25),and then is reheated in the pipe ducting 35 before being expandedthrough the low pressure turbine so as to drive the low pressure turbinecompressor rotor (I I, l2, l3) and, through the reduction gear 31 andshaft 23, the tractor propeller 42, 43.

Any residual energy in the exhaust gases from the low pressure turbinemay be used, in known manner, as a propulsion jet.

This application is related to my oo-pending application Serial No.558,024, filed October 10,

4 1944, now patent No. 2,504,414 in that it also relates to doublecompound internal combustion turbines.

What I claim as my invention and desire to secure by Letters Patent is:

1. In a double compound internal combustion turbine aero engineincluding a rotor comprising alow pressure compressor and a low pressureturbine and a rotor comprising a high pressure compressor and a highpressure turbine, said rotors being independently rotatable andcoaxially adjacent so that the low pressure turbine, low pressurecompressor, high pressure compressor and high pressure turbine are inthat serial order from the rear to the front of the engine (consideredin relation to the direction of flight), the air entry being at the rearend of the low pressure compressor and the low pressure turbineexhausting rearwardly without terminal reversal of flow, combustionmeans annularly disposed between the high pressure compressor and thehigh pressure turbine, ducting interconnecting said compressors,turbines and combustion means, said ducting being disposed annularlyabout the common axis of the rotors and so constructed and arranged asto provide a generally axial flow path through the low and high pressurecompressors, combustion means and high and low pressure turbines in thatorder with reversal of the general direction of flow between theturbines, the improvement that comprises reduction gearing locatedbetween adjacent ends of the two rotors and driven by the low pressurerotor, a power transmission shaft driven by said reduction gear andextending axially through the high pressure rotor to the front of theengine and a tractor propeller driven by said power transmission shaft.

2. In an aircraft propulsion plant of the double compound gas turbinetype which includes a highpressure turbine, high-pressure andlow-pressure compressors, and a low pressure turbine all in axialalignment along the intended direction of flight, a combustion chamberand ducting defining a path from the compressors to the combustionchamber and from the combustion chamber to the turbines, thelow-pressure turbine being in the rear end and the compressors beingbetween the turbines, the improvement that comprises a tractor propellerat the front end of the plant and shaft extending rearwardly from thepropeller along the plant axis, a, shaft extending forwardly from thelow-pressure turbine along the same axis, and reduction gearingconstituting a driving connection from said turbine shaft to saidpropeller shaft, said gearing being located along the plant axisintermediate the remote axial extremities of the compressors.

VJILLIANI REDE HAVTHORNE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,959,795 Lysholm May 22, 19342,050,349 Lysholm et al Aug. 11, 1936 2,243,467 Jendrassik May 27, 19412,292,288 Pescara Aug. 4, 1942 2,326,072 Seippel Aug. 3, 1943 2,409,446Pavlecka Oct. 15, 1946 2,411,227 Planiol et al Nov. 19, 1946 2,454,738Hawthorne Nov. 23, 1948 2,504,414 Hawthorne Apr. 18, 1950

